1. Field of the Invention
The present invention relates to a photodetector using nanoparticles. More particularly, the present invention relates to a photodetector using nanoparticles with organic material-capped surfaces synthesized by a wet colloidal process, or close-packed nanoparticles formed by removal of surface-capped organic materials.
2. Description of the Related Art
As a conventional photodetector 10 using quantum effects, a structure taking advantage of quantum well (QW) effects is well known to those skilled in the art, as shown in FIG. 1. However, where light is irradiated in the direction vertical to QW layer 11 (direction a), optical pumping may occur (due to influence of an electrical field present in the vertical direction) relative to the light direction (i.e., in the direction horizontal to the QW layer 11) and as a result, high quantum efficiency is not obtained in the planar direction (direction a), which is present in a bulk form. Conversely, where light is irradiated in the direction horizontal to QW layer 11 (direction b), even though optical pumping may occur due to effects of quantum effects, it is difficult to collect light on a QW region that is physically several nanometers in size, thereby resulting in poor light receiving efficiency. In addition, the resulting photocurrent flows in the following route: quantum well (QW) layer 11→quantum barrier (QB) 12→quantum well (QW) layer 13, as shown in FIG. 2, thereby leading to lowered efficiency. Where it is desired to detect a wavelength in a far infrared region using such a conventional photodetector, several hundred QW layers 11, serving as channels, are required, thus necessitating a prolonged period of time and highly expensive equipment in fabricating the photodetector.
In the case of the photodetector made up of quantum dots, as has recently been reported, the quantum dots self-assemble when prepared by vapor phase methods such as Metal Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE). The basic structure of the quantum dot photodetector synthesized by such vapor phase methods takes a form in which self-assembled quantum dots are incorporated into a quantum well active layer in a conventional quantum well photodetector p-n structure. In this connection, the photodetector having such a structure suffers from the following problems:
1) Since quantum dots are not connected to one another and thus independently present due to characteristics inherent to synthesis methods used, an existing quantum barrier makes it difficult to efficiently generate photocurrent even when light is received and electrons are activated.
2) Since self-assembled quantum dots, which are prepared by MOCVD or MBE, have inevitably a barrier layer after formation of a monolayer, the thickness of a light-receiving region is too small, which in turn results in light scattering and very low efficiency of receiving light. In particular, when it is desired to receive infrared light, the active layer should have a thickness of several nanometers, but it is not easy to achieve this thickness.
3) Finally, the p-n structure entails complicated fabrication processes and poor efficiency of a light-receiving window.